LASER TRACKER HAVING TARGET-SEEKING FUNCTIONALITY

• US 20160252619A1
• Filed: 07/16/2014
• Published: 09/01/2016
• Est. Priority Date: 07/16/2013
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: MARKENDORF, Albert, BCKEM, Burkhard
• Granted Patent: US 10,048,379 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 5/008 using coordinate measuring machines
• CPC Class Codes: G01C 1/04 combined with cameras
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 17/89 for mapping or imaging

Abstract

Some embodiments of the invention relate to a laser tracker for continuously tracking a reflective target and for determining the position of the target, comprising a base that defines a vertical axis and a beam-deflecting unit for emitting measurement radiation. The beam-deflecting unit can be pivoted about the vertical axis and a tilt axis in relation to the base in a motorized manner and a measurement axis is defined by an emission direction of the measurement radiation. The laser tracker may have a fine distance measurement unit for precisely determining a distance to the target, an angle measurement functionality for determining an orientation of the beam-deflecting unit in relation to the base, and a target-seeking unit. The target-seeking unit has illuminating means, a camera having a position-sensitive detector for detecting illumination radiation reflected by the target, and a control and evaluating unit having seeking functionality for finding the target.

Claims

1-51. -51. (canceled)

52. A laser tracker for continuously tracking a reflective target and for determining the position of the target, the laser tracker comprising:

a base defining a vertical axis,

a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target, with the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and a measurement axis being defined by an emission direction of the measurement radiation,

a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target with the help of detecting the measurement radiation reflected by the target,

a fine distance measurement unit for precisely determining the distance to the target with the help of the measurement radiation,

an angle measuring functionality for determining an orientation of the beam deflecting unit relative to the base and

a target-seeking unit comprising;

at least a first and a second means of illumination with a fix distance to one another defining a first basic length for illuminating the target with electromagnetic illumination radiation,

a camera defining a field of view with a position-sensitive detector, wherein

the camera, regarding its optical axis, is offset regarding the measurement axis,

the camera can be used to acquire a picture,

in the picture, at least a part of the illumination radiation of the first and the second means of illumination reflected by the target can be acquired as a first and a second light spot, and

a control and evaluating unit with seeking functionality for finding the target depending on the light spots so that the measurement radiation can be directed towards the target based on finding the target,

wherein when executing the seeking functionality,

at least one picture position is determined depending on the first and/or the second light spot on the detector,

a piece of parallax correction information is determined by picture processing the picture taken, the information taking into account a separation of the light spots and depending on a distance of the two light spots to one another, and

the process of finding the target is performed using the at least one picture position and depending on the parallax correction information, so that a parallax defined by the measurement axis and the optical axis of the camera is taken into account.

53. The laser tracker according to claim 52, wherein:

the means of illumination are designed in such a way that the electromagnetic illumination radiation can be emitted divergently with a wavelength in the infrared range, with

the means of illumination being designed as light-emitting diodes for emitting light with a wavelength in the infrared range,

the intensity of the illumination radiation being dynamically variable, and/or

the camera being designed in such a way that essentially only infrared illumination radiation can be acquired, specifically with the camera being equipped with a filter, especially for the essentially exclusive transmission of the infrared radiation to the position-sensitive detector.

54. The laser tracker according to claim 52, wherein:

the target-seeking unit is equipped with at least a third and a fourth means of illumination with a basic length differing from the first basic length, used instead of the first and the second means of illumination or in addition to these for illuminating the target, with the means of illumination to be used being selected depending on the known nature of the target when the seeking functionality is executed.

55. The laser tracker according to claim 52, wherein:

an overlap of the illumination radiation cross-sectional forms of the first and the second means of illumination, acquired in a picture of a camera, impairing a separate picture position determination depending on the respective light spot, is avoided or resolved by

the process of illuminating the target by the first and the second means of illumination and the process of acquiring a single light spot position created by the above being performed at different times when executing the seeking functionality,

the first and the second means of illumination each being capable of emitting illumination radiation of different wavelengths and/or polarization, separable by the camera, with the help of filters,

the individual cross-sectional forms being segmented by picture processing the picture, using edge detection, segmenting circular shapes, circular shapes with a defined diameter or diameter interval, specifically using Circular Hough Transformation (CHT) or scale-invariant kernel operators, and/or

matching the light spot form acquired in the picture from the overlapping individual illumination radiation cross-sectional forms with a stored sample based on a best-fit method, with sub-pixel accuracy, with the respective individual light spot position of the illumination radiation of the respective means of illumination acquired in the picture being determined on the basis of the harmonized position of the sample in the picture, with sub-pixel accuracy, with at least one, especially, two pieces of information being co-stored for the stored sample that permits to derive sample-internally defined sample positions to be used for finally determining the respective light spot position within the sample, specifically with the information being the sample-internally defined sample position or a defined sample position determination algorithm.

56. The laser tracker according to claim 52, wherein:

the laser tracker includes a calibration functionality, during the execution of which a referenced assignment of picture positions and parallax correction information to roughly approximated positions of the target is developed and stored and/or the known position of the means of illumination relative to the optical axis and/or measurement axis and/or the fix basic length of the means of illumination and/or the known position of the optical axis relative to the measurement axis are determined, with, when executing the calibration functionality,

the fine distance measurement unit targeting and measuring a target provided in different positions with the help of the measurement radiation,

for every position of the target the at least one picture position being determined, and

the measurement of the target and the at least one picture position and parallax correction information determined in this regard being used to derive the relative positions of the means of illumination regarding the measurement axis and the basic length.

57. The laser tracker according to claim 52, wherein:

the control and evaluating unit includes a picture position determination functionality, during the execution of which a picture position is determined with the help of picture processing in a picture acquired by the camera in such a way that the picture position represents the position in the picture of an illumination radiation cross-sectional form acquired in the picture, with the help of center of gravity calculation on the basis of the light spot form acquired in the picture, with the help of a brightness and/or contrast analysis, and/or

by matching the illumination radiation cross-sectional form acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, with at least one picture position of the illumination radiation acquired in the picture being determined on the basis of the harmonized position of the sample in the picture, with sub-pixel accuracy, with one piece of information being co-stored for the stored sample that permits to derive sample-internally defined sample positions to be used for finally determining the picture position within the sample, specifically with the information being the sample-internally defined sample position or a defined sample position determination algorithm, such as a sample center of gravity determination algorithm, for instance.

67. A method for finding a target with the help of a laser tracker according to claim 52, with the laser tracker being equipped with:

a base defining a vertical axis and

a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target, with

the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and

a measurement axis being defined by an emission direction of the measurement radiation, and

a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target by detecting the measurement radiation reflected by the target,

as well as with

an illumination of the target with electromagnetic illumination radiation by at least a first and a second means of illumination, wherein a fix distance to one another defining a first basic length,

a position-sensitive acquisition of at least one picture with a camera positioned at the laser tracker and defining a field of view, with, in the picture, at least a part of the illumination radiation of the first and the second means of illumination reflected by the target being acquired as a first and a second light spot,

a process of finding the target on the basis of analyzing the acquired light spots and orienting the measurement radiation towards the target based on finding the target, wherein;

a determination of at least one picture position on the detector of the camera depending on the first and/or the second light spot,

a determination of a piece of parallax correction information by picture processing the picture taken, within the framework of which a separation of the light spots is taken into account and that depends on a distance of the two light spots to one another,

finding the target using the at least one picture position and depending on the parallax correction information so that a parallax defined by the measurement axis and the optical axis of the camera is taken into account.

69. The method according to claim 67, wherein:

determining a, particularly azimuth angle-related, deviation between the direction of the measurement axis and the direction to the target using the at least one picture position and depending on the parallax correction information, with

determining a roughly approximated distance to the target, based on a stored referenced assignment of a piece of parallax correction information to roughly approximated distances and/or

deriving at least one, particularly a first and a second, target direction to the target and, depending on the target directions, determining a roughly approximated position of the target, using a determined roughly approximated distance, with the help of triangulation, or

determining a roughly approximated position of the target on the basis of a stored reference table, where picture positions and parallax correction information are assigned to roughly approximated positions of the target.

70. The method according to claim 67, wherein:

an automatic orientation of the beam deflecting unit on the basis of the search result, depending on a roughly approximated position of the target determined in so doing so that the measurement radiation hits the target and can be detected with the help of the fine targeting detector.

71. The method according to claim 67, wherein:

a piece of parallax correction information is determined by picture processing the picture taken in such a way that

a distance of two picture positions on the detector is determined, which is determined based on a separate picture position determination depending on the first and the second light spot in each case,

by means of matching the illumination radiation cross-sectional form acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, a piece of size information regarding the illumination radiation cross-sectional form acquired in the picture is determined based on the harmonized form of the sample in the picture, with sub-pixel accuracy, with a piece of information being co-stored for the stored sample that permits to derive a sample-internally defined piece of information regarding the extent of the light spot separation to be used for finally determining the parallax correction information, specifically with the information being the sample-internally defined parallax correction information or a defined parallax correction information determination algorithm, or

a geometrical characteristic variable is determined for the illumination radiation cross-sectional form acquired in the picture,

and/or a process of finding the target is performed using several first and second light spots, by averaging using a roughly approximated distance to the target and/or roughly approximated position of the target determined depending on the above in each case, and/or additionally or alternatively to illuminating the target by the first and the second means of illumination, illumination by a third and a fourth means of illumination with a basic length differing from the first basic length.

72. A non-transitory computer program product with program code stored on a machine-parsable medium for controlling and implementing the method, respectively, according to claim 67.

58. Laser tracker for continuously tracking a reflective target and for determining the position of the target with

a base defining a vertical axis,

a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target as reflected illumination radiation bundle, with

the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and

a measurement axis being defined by the emission direction of the measurement radiation,

a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target by detecting the measurement radiation reflected by the target,

a fine distance measurement unit for precisely determining the distance to the target with the help of the measurement radiation, and

an angle measuring functionality for determining an orientation of the beam deflecting unit relative to the base, wherein:

a target-seeking unit with

at least a first means of illumination for illuminating the target with electromagnetic illumination radiation,

at least a first and a second optical mapping unit each defining a field of view, wherein

the optical units can be used to acquire a picture,

the optical mapping units are characterized by a fix distance to one another, defining a first basic length, and

the optical mapping units are positioned so close to the first means of illumination, that both optical mapping units are within the cross-section of the illumination radiation bundle reflected by the target,

at least one position-sensitive detector,

an optical axis, with the optical axis being offset regarding the measurement axis, and

a control and evaluating unit with seeking functionality for finding the target depending on a first and a second light spot so that the measurement radiation can be directed towards the target based on finding the target,

with, when executing the seeking functionality,

one part of illumination radiation of the first means of illumination reflected by the target being acquired by the first optical mapping unit as a first light spot and by the second optical mapping unit as a second light spot in the picture,

at least one picture position being determined depending on the first and/or second light spot on the detector,

a parallax correction information being determined by picture processing the picture taken, where a separation of the light spots is taken into account and that depends on a distance of the two light spots to one another, and

the process of finding the target being performed using the at least one picture position and depending on the parallax correction information, so that a parallax defined by the measurement axis and the optical axis of the target-seeking unit is taken into account.

59. The laser tracker according to claim 58, wherein:

the target-seeking unit is equipped with at least a third and a fourth optical mapping unit each defining a field of view with a basic length differing from the first basic length, used instead of the first and the second optical mapping unit or additionally to these units for acquiring illumination radiation reflected by the target, with, when the seeking functionality is executed, a selection of the optical mapping units to be used being performed depending on a known nature of the target.

60. The laser tracker according to claim 58, wherein:

the laser tracker includes a calibration functionality that, when executed, determines and stores a referenced assignment of picture positions and parallax correction information to roughly approximated positions of the target and/or determines the known position of the optical axes of the optical mapping units relative to the means of illumination and/or measurement axis and/or the fix basic length of the optical mapping units and/or the known position of the optical axis of the target-seeking unit relative to the measurement axis, with, when executing the calibration functionality,

the fine distance measurement unit targeting and measuring a target provided in different positions with the help of the measurement radiation,

the at least one picture position being determined for every position of the target, and

the relative positions of the target-seeking unit regarding the measurement axis and the basic length being determined based on the measurement of the target and the at least one picture position and parallax correction information determined in this regard.

61. The laser tracker according to claim 58, wherein:

an overlap of illumination radiation cross-sectional forms of the first means of illumination acquired within a picture impairing a separate picture position determination depending on the respective light spot is avoided or resolved by

the acquisition of an individual light spot position, when executing the seeking functionality, by the optical mapping units being performed in a staggered manner,

the first means of illumination being capable of emitting illumination radiation of a different wavelength and/or polarization separable by the optical mapping units), with the help of filters,

segmenting the individual cross-sectional forms through picture processing the picture, using edge detection, segmenting circular shapes, circular shapes with a defined diameter or diameter interval, specifically using Circular Hough Transformation (CHT) or scale-invariant kernel operators, and/or

matching the light spot form created by the overlapping individual illumination radiation cross-sectional forms acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, with the harmonized position of the sample in the picture being used to determine the respective individual light spot position of the first and the second light spot acquired in the picture, with sub-pixel accuracy, with at least one pieces of information being co-stored for the stored sample that permit to derive sample-internally defined sample positions to be used for finally determining the picture position within the sample, specifically with the information being the sample-internally defined sample position or a defined sample position determination algorithm.

62. The laser tracker according to claim 58, wherein:

the control and evaluating unit includes a picture position determination functionality that, when executed, determines a picture position in a picture acquired by an optical mapping unit with the help of picture processing in such a way that the picture position represents a position in the picture of an illumination radiation cross-sectional form acquired in the picture,

with the help of center of gravity calculation based on the light spot form acquired in the picture, with the help of a brightness and/or contrast analysis, and/or

by matching the illumination radiation cross-sectional form acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, with at least one picture position of the illumination radiation acquired in the picture being determined on the basis of the harmonized position of the sample in the picture, with sub-pixel accuracy, with one piece of information being co-stored for the stored sample that permits to derive sample-internally defined sample positions to be used for finally determining the picture position within the sample, specifically with the information being the sample-internally defined sample position or a defined sample position determination algorithm, such as a sample center of gravity determination algorithm, for instance.

63. The laser tracker according to claim 58, wherein:

the control and evaluating unit is configured in such a way that, when executing the seeking functionality, an azimuth angle-related deviation of the direction of the measurement axis from the direction to the target is determined using the at least one picture position and depending on the parallax correction information, with

a roughly approximated distance to the target being determined, based on a stored referenced assignment of parallax correction information to roughly approximated distances and/or

at least one direction being derived and a roughly approximated position of the target being determined depending on the target direction, using a determined roughly approximated distance, with the help of triangulation, or

a roughly approximated position of the target being determined on the basis of a stored referenced assignment of picture positions and parallax correction information to roughly approximated positions.

64. The laser tracker according to claim 58, wherein:

the beam deflecting unit can be controlled using the control and evaluating unit in such a way that an automatic orientation of the measurement radiation is performed on the basis of the search result so that measurement radiation hits the target and can be detected using the fine targeting detector.

65. The laser tracker according to claim 58, wherein:

the parallax correction information is determined by processing the picture taken in such a way that

a distance of two picture positions on the detector is determined, which are determined on the basis of a separate picture position determination depending on the first and the second light spot in each case,

by matching the illumination radiation cross-sectional form acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, with a piece of size information regarding the illumination radiation cross-sectional form acquired in the picture being determined on the basis of the harmonized form of the sample in the picture, with sub-pixel accuracy, with a piece of information being co-stored for the stored sample that permits to derive a sample-internally defined piece of information regarding the extent of light spot separation to be used for the final determination of the parallax correction information, specifically with the information being the sample-internally defined parallax correction information or a defined parallax correction information determination algorithm, or

a geometrical characteristic variable is determined for the illumination radiation cross-sectional form acquired in the picture.

66. The laser tracker according to claim 58, wherein:

the laser tracker is equipped with

a support pivoting around the vertical axis relative to the base in a motorized manner and defining the tilt axis and

a targeting unit designed as a beam deflecting unit, pivoting around the tilt axis relative to the support in a motorized manner, with a telescopic unit for emitting the measurement radiation and for receiving at least a part of the measurement radiation reflected by the target.

68. A method for finding a target using a laser tracker according to claim 58, with the laser tracker being equipped with:

a base defining a vertical axis and

a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target, with

the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and

a measurement axis being defined by the emission direction of the measurement radiation, and

a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target by detecting the measurement radiation reflected by the target,

as well as with

an illumination of the target with electromagnetic illumination radiation by at least a first means of illumination, wherein;

a position-sensitive acquisition of at least one picture with a first and a second optical mapping unit positioned at the laser tracker and each defining one field of view as part of a target-seeking unit, wherein a fix distance to one another defining a first basic length, with, in the picture, at least a part of the illumination radiation of the first means of illumination reflected by the target being acquired as the first light spot by the first optical mapping unit and as the second light spot by the second optical mapping unit,

finding the target on the basis of analyzing the acquired light spots and orienting the measurement radiation towards the target based on finding the target,

a determination of at least one picture position on the at least one detector, the optical mapping units project at least a part of the illumination radiation reflected by the target to, depending on the first and/or the second light spot,

a determination of a piece of parallax correction information by picture processing the picture taken, within the framework of which a separation of the light spots is taken into account and that depends on a distance of the two light spots to one another,

finding the target using the at least one picture position and depending on the parallax correction information so that a parallax defined by the measurement axis and the optical axis of the target-seeking unit is taken into account.

73. A laser tracker for continuously tracking a reflective target and for determining the position of the target with

a base defining a vertical axis,

a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target, with

the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and

a measurement axis being defined by an emission direction of the measurement radiation,

a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target by detecting the measurement radiation reflected by the target,

a fine distance measurement unit for precise distance determination to the target with the help of the measurement radiation,

an angle measurement functionality for determining an orientation of the beam deflecting unit relative to the base, and

a target-seeking unit with

means of illumination for illuminating the target with electromagnetic illumination radiation,

a camera defining a field of view with a position-sensitive detector, with

the camera, regarding its optical axis, being offset to the measurement axis,

the camera being used in order to acquire a picture,

the picture being used in order to determine a picture position X using the illumination radiation reflected by the target, and

a control and evaluating unit including a seeking functionality for finding the target, configured in such a way that, when executing the seeking functionality, the process of finding the target depends on the picture position so that the measurement radiation can be directed towards the target on the basis of finding the target, wherein:

the target-seeking unit is equipped with an omnidirectional means for target distance determination for sending and receiving a measurement signal that can be used to determine a roughly approximated distance to the target by capturing a time of flight, phase information, and/or strength of the measurement signal, when executing the seeking functionality, and

the process of finding the target is performed depending on the picture position X using the determined roughly approximated distance so that a parallax defined by the measurement axis and the optical axis of the camera is taken into account.